The present invention relates generally to the field of optics and more specifically to the field of measurement and testing of the stability of photodetectors.
The determination of the long-term stability of a photodetector requires the measurement of the response, e. g. photocurrent, of the photodetector to a known or constant optical flux. The usual procedure for assuring that the measurement flux is constant is physically to substitute a reference detector, known to be stable, for the detector under test and to use the response of the reference detector to set the optical flux level. The problem with this method is that it is impossible mechanically to reproduce the positions of the photodetectors in the optical flux to a high precision, especially if a number of test detectors are to be monitored concurrently. Practically, with this foregoing method measurement precision on the order of 1% is not possible.